Superfinishing is a process used to remove small amounts of stock from a workpiece. Superfinishing is commonly performed after grinding to achieve the following objectives: removing an amorphous surface layer produced by grinding, decreasing surface roughness, improving part geometry, and providing a desired surface topography. The removal of the amorphous layer improves the wear resistance of the workpiece. The decreased surface roughness further increases the load-bearing capability of the workpiece, and the characteristic topographical pattern aids in oil retention.
Superfinishing is generally performed using a vitreous-bonded microabrasive tool formed of abrasive particles in a bond matrix. “Microabrasive” tools are generally defined as abrasive tools wherein the size of the abrasive particles is 240 grit (63 micrometers or microns) or finer. Microabrasive tools are generally manufactured according to one of a couple well-established processes.
According to one process, abrasive grains and a bonding material are mixed with binders assisted by a small amount of liquid (e.g., less than 4% by weight). The liquid usually is water. This “semi”-dry mix then is cold pressed to shape and green density. Finally, the green form is fired to produce a microabrasive tool.
Another even-older process for making microabrasive products is the so-called “puddle” process. According to the puddle process, the abrasive grains and the bonding material are mixed with enough water to produce a pourable slurry. Consequently, the puddle process is considered a wet process. The slurry is poured into a mold and allowed to dry. The dried mixture is then fired to produce an abrasive tool.
One advantage of the puddle process is that by mixing the abrasive grains and the bonding material in a slurry, a better distribution of the abrasive grains and the bonding material (i.e., better mixing) can be obtained compared with what is typically obtained with dry or semi-dry mixing.
Nevertheless, in both of these forming methods, abrasive products are produced in which particles of the bonding material and the abrasive are nonuniformly dispersed. In the semi-dry process, this nonuniform dispersion is due to incomplete mixing of the bonding material and the abrasive grains. In the wet process, the nonuniformity is generally due to settling of the bonding material and the abrasive grains relative to one another.